Although I don't see eye tracking in games as 'the next big thing' in any sense (the few I've tried were severely lacking in the fun department), I would be interested to try playing Soma with this.
Soma had some flaws to be sure, but damn did it do some things really well. I'd highly recommend it - eye tracking or no.
One great application I can think of is depth of field adjustment. Some games have depth of field simulation, which makes far away scenery blurry. Personally I always disable it because I think it belongs to the uncanny valley: it's nice on screenshots, but it doesn't work so well in-game because the focus doesn't change with where/what you're looking at. Eye tracking, by making this feature dynamic, would I think enhance 3D rendering for relatively cheap.
Good use of eye tracking could also allow for foveated rendering, drawing the out-of-focus areas with lower resolution and leaving more time to render the areas of interest.
Soma had some flaws to be sure, but damn did it do some things really well. I'd highly recommend it - eye tracking or no.